A wide variety of testing apparatuses for communications systems have evolved along with the communicating systems they serve. Generally speaking as the complexities of the systems increase, the methods and devices for determining proper systems operation also grow in complexity.
Typical of a system and method for monitoring the performances of a channel is shown in U.S. Pat. No. 3,694,643. Pseudorandom noise sequence generators are fabricated to provide signals transmitted simultaneously with a data signal to determine the cross-correlation between the data signal and the generator signal. While a great deal of detail is not stated regarding the pseudorandom noise sources, it appears that they are fixed and not reprogrammable and may be of a somewhat high degree of complexity. The apparatus and method for measuring envelope delay of U.S. Pat. No. 3,842,247 has a computer generating signals for controlling the signal generator for adjusting loss in a reference pass to equal the loss experienced by a signal propagating through the facility under test at the frequency of interest. The simulation of the loss by the general purpose computer appears to be effective for the specific application disclosed and apparently does not require a single common time base with the information flow of the information signal. U.S. Pat. No. 4,074,201 has an analyzer and noise estimation relying upon a reference source amplifier and comparator for producing a reference signal for comparison with an input signal. The method and circuit arrangement of U.S. Pat. No. 4,322,857 has a test pulse generator driving a broadband noise generator that feeds the test signal at the input of the high frequency stage of a radio receiver. Only the general broad function that a pulse sequence is generated is disclosed. The details of the test pulse generator are not elaborated on. The apparatus of U.S. Pat. No. 4,412,348 shows a test equipment to determine the linearity of an FM transmitter and relies upon a single amplitude modulation generator signal source that produces an amplitude modulated signal of known varying amplitudes.
Some of the highly sophisticated data processing techniques for the more sophisticated information content need more to be validated and verified to provide meaningful information regarding the systems's readiness. Finely tuned signal discrimination, error checking and spurious signal detection capabilities must be routinely checked and validated. Part of this validation process should have the detection and identification of error signals, as opposed to information signals, so that they can properly be compensated for and discarded. Error signals of the type likely to influence some sophisticated signals might require a complicated test device and, as such, may be unduly costly and of doubtful long term reliability due to their complexity.
Thus, there exists in the state of the art a continuing need for a validation testing device which generates erroneous data within the envelope of an expected information signal that is precisely determinable and readily reprogrammable to provide operators and technicians an indication of the current operational status of complex communications systems.